<scp>Alpine:</scp> Partial Unlabeled Graph Alignment

Several applications call to align the nodes of two graphs in a way that minimizes a distance function.In practicality, the graphs to be aligned often have unequal orders (i.e., numbers of vertices) and no auxiliary labels or attributes; we refer to this problem as partial unlabeled graph alignment.Some proposals to address this problem add dummy nodes to the smaller graph to even the orders and align the ensuing graphs or employ embeddings such as GNNs, which yield ad hoc node representations.Unfortunately, as we show, an optimal solution to equal-order graph alignment using dummy nodes does not imply an optimal solution to partial graph alignment.To address this deficiency, in this paper, we propose Alpine, a Partial Unlabeled Graph Alignment algorithm that solely peruses the graphs' adjacency matrices, guided by a tailored objective function inspired by best-of-breed shape matching techniques and a state-ofthe-art optimization method.Extensive experiments demonstrate that Alpine consistently surpasses state-of-the-art graph alignment methods in solution quality across all benchmark datasets.